1. Field of the Invention
The present invention relates to a photo-detecting device and, more particularly, to one which is suitable for monitoring comparatively large objects and targets, for instance, traffic roads, airports and so on.
2. Brief Description of the Prior Art
As such sorts of photo-detecting device as mentioned above, following two types of devices have been investigated:
a) A first type is a device wherein a photo-detecting cell is rotated by a driving motor. PA1 b) A second type is a device wherein many of individual photo-detecting cells are allocated so that the optical axes of photo-detecting cells orient to relatively dispersed directions. PA1 a movable plate monolithically formed in a semiconductor substrate, PA1 a torsion bar monolithically formed in the semiconductor substrate to axially support the movable plate on the semiconductor substrate, allowing the movable plate freely to swing and to rock with respect to the semiconductor substrate, PA1 a driving coil formed on peripheries of the movable plate, PA1 a generating means of a magnetic field for applying a static magnetic field to the driving coil, and PA1 a photo-detecting cell formed on the movable plate; PA1 wherein a current introduced to flow through the driving coil generates a force to move the movable plate in response to the force to vary an orienting direction of the optical axis of the photo-detecting cell. PA1 an outer movable plate monolithically formed in a semiconductor substrate, PA1 a first torsion bar monolithically formed in the semiconductor substrate to support axially the outer movable plate on the semiconductor substrate, allowing the outer movable plate freely to swing and to rock with respect to the semiconductor substrate, PA1 an inner movable plate monolithically formed inside the outer movable plate, PA1 a second torsion bar monolithically formed inside the outer movable plate to support axially the inner movable plate on the outer movable plate, allowing the inner movable plate freely to swing and to rock with respect to the outer movable plate, of which axial direction orthogonally intersects another axial direction of the first torsion bar, PA1 a first driving coil formed on peripheries of the outer movable plate, PA1 a second driving coil formed on peripheries of the inner movable plate, PA1 a first generating means of a magnetic field for applying a static magnetic field to the first driving coil, PA1 a second generating means of another magnetic field for applying another static magnetic field to the second driving coil, and PA1 a photo-detecting cell formed on the inner movable plate; PA1 wherein currents introduced to flow through the first and the second driving coils generate forces to move the outer and inner movable plates in response to the forces to vary an orienting direction of the optical axis of the photo-detecting cell.
However, the device of the first type encounters with problems that the device is structurally too large to enable a high-speed operation while it is unrealistic from a manufacturing cost point of view.
On the other hand, the device of the second type mentioned above also encounters with another problem that differences in cell characteristics induced between each of the photo-detecting cells are required to be compensated.